Locking mechanism for webbing retractor

ABSTRACT

A lock mechanism for a webbing retractor prevents an occupant restraining webbing from being wound off from a webbing takeup shaft when a vehicular emergency occurs. The lock mechanism is provided with a member to which the rotational force of the takeup shaft is transmitted through frictional contact and which cancels the locked state of the lock mechanism when the takeup shaft rotates in the webbing wind-up direction. Accordingly, it is possible to prevent the webbing from being gradually wound up when the vehicle is running thus avoiding any possibility of causing the webbing to undesirably tighten against the body of the occupant.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lock mechanism for a webbingretractor employed in a seatbelt system designed to protect an occupantof a vehicle when an emergency situation occurs, the lock mechanismbeing adapted to prevent an occupant retraining webbing from being woundoff at the time of such an emergency.

2. Description of the Prior Art

A typical seatbelt system includes a webbing retractor into which anoccupant restraining webbing is wound up from one end thereof by meansof a predetermined biasing force and which incorporates a lock mechanismadapted to prevent the webbing from being wound off when a vehicularemergency occurs.

The lock mechanism has a lock ring provided in such a manner that thelock ring rotates together with the rotation of a webbing takeup shaftin the webbing wind-off direction and a resilient member interposedbetween the lock ring and the takeup shaft. Thus, when a vehicularemergency occurs, an acceleration sensing means causes the lock ring tobe subjected to resistance which acts against the rotation of the lockring, and a lock member which rotates together with the takeup shaft istherefore driven with a lag in terms of rotation of the lock ringrelative to the takeup shaft and is engaged with lock teeth formed on aframe (see specifications of Japanese Patent Publication No. 16,969/1969and Japanese Patent Laid-Open No. 1,115/1972).

This type of conventional lock mechanism, however, suffers from thefollowing problems. Namely, when a vehicle is running on a rough roadwith many irregularities, the acceleration sensing means may beundesirably kept in an operative state. If so, the lock mechanism isunfavorably maintained in its locked state, which fact makes itimpossible for the occupant to wind off the webbing. Further, duringsuch running on a rough road, the occupant is repeatedly bumped up anddown by the vibration of the vehicle, and the webbing is therebyrepeatedly wound in and out. As a result, every time the webbing iswound in, the position of engagement between the lock member and thelock teeth gradually advances, so that the webbing is gradually wound upinto the webbing retractor, which fact may unfavorably increase thepressure applied to the body of the occupant.

SUMMARY OF THE INVENTION

In view of the above-described situation, it is a primary object of thepresent invention to provide a lock mechanism for a webbing retractorwhich involves no risk of the webbing being gradually wound up into thewebbing retractor even when a given length of the webbing is repeatedlywound in and out.

To this end, the invention provides a lock mechanism for a webbingretractor in which a limiting member is pivoted by means of therotational force of the webbing takeup shaft through a frictionalcontact means in such a manner that, when the takeup shaft rotates inthe webbing wind-up direction, the limiting member prevents the lockring from being subjected to the resistance which is applied by theacceleration sensing means and which acts against the rotation of thelock ring.

Accordingly, when the webbing is wound up, the limiting member preventsthe application of the above-described resistance to the lock ring bythe acceleration sensing means and allows the lock ring to rotate. Inconsequence, the lock ring is rotated in the webbing wind-off directionby the action of the resilient member interposed between the takeupshaft and the lock ring. Accordingly, in the next webbing wind-offoperation, the lock ring engages with the acceleration sensing means atthe same position as that where the previous locking condition wasestablished, or engages with the acceleration sensing means in the statewherein the lock ring has been rotated in the webbing wind-offdirection. Therefore, even when a given length of the webbing isrepeatedly wound in and out many times, there is no risk of the webbingbeing gradually wound up.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description ofthe preferred embodiments thereof, taken in conjunction with theaccompanying drawings, in which like reference numerals denote likeelements, and in which:

FIG. 1 is an exploded perspective view of a webbing retractor to which afirst embodiment of the lock mechanism according to the presentinvention is applied;

FIG. 2 is a side elevational view of a webbing takeup shaft employed inthe webbing retractor shown in FIG. 1;

FIG. 3 is a front elevational view of a part of the lock mechanism,which shows the relationship between lock plates and aninternally-toothed rachet wheel;

FIG. 4 shows the operation of the part of the lock mechanism shown inFIG. 3;

FIG. 5 illustrates the way in which a lock ring and a torsion coilspring employed in the lock mechanism are assembled together;

FIG. 6 is a sectional view of a part of the lock mechanism, which showsthe way in which the webbing takeup shaft and a rotating wheel areassembled together;

FIGS. 7(A) to 7(E) illustrate the operations of a limiting plate, anactuator and their associated elements which are employed in the firstembodiment;

FIG. 8 is a perspective view of a limiting plate employed in a secondembodiment of the present invention;

FIG. 9 is a perspective view of a spring plate employed in a thirdembodiment of the present invention;

FIG. 10 is an exploded perspective view of a webbing retractor to whicha fourth embodiment of the present invention is applied;

FIG. 11 is a perspective view of a frame employed in a fifth embodimentof the present invention;

FIG. 12 is a perspective view of a limiting plate employed in the fifthembodiment;

FIG. 13(A) is a side elevational view of the fifth embodiment;

FIG. 13(B) shows the operation of the fifth embodiment;

FIG. 14 is a perspective view of a limiting plate employed in a sixthembodiment of the present invention;

FIG. 15 is a perspective view of a spring plate employed in a seventhembodiment of the present invention;

FIG. 16 is an exploded perspective view of a webbing retractor to whichan eighth embodiment of the present invention is applied;

FIG. 17 is an exploded perspective view of a ninth embodiment of thepresent invention;

FIG. 18 is a perspective view of a rotating cap employed in a tenthembodiment of the present invention;

FIG. 19 is a perspective view of a friction spring employed in the tenthembodiment;

FIG. 20 is a perspective view of a cover employed in the tenthembodiment;

FIG. 21 is a sectional view of a part of the tenth embodiment, whichshows the way in which the webbing takeup shaft and the rotary cap areassembled together;

FIGS. 22 (A) to 22(E) illustrate the operations of the friction spring,the actuator and their associated elements which are employed in thetenth embodiment;

FIG. 23 is a side elevational view of a friction spring employed in aneleventh embodiment of the present invention;

FIG. 24 is a side elevational view of a part of a twelfth embodiment ofthe present invention;

FIG. 25 is an exploded perspective view of a webbing retractor to whicha thirteenth embodiment of the present invention is applied;

FIGS. 26(A) to 26(E) illustrate the operations of the limiting member,the actuator and their associated elements employed in the thirteenthembodiment;

FIGS. 27(A) and 27(B) are sectional views taken along the lineVIII--VIII of FIG. 26(A); and

FIG. 28 is a front elevational view of a part of a fourteenth embodimentof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is an exploded perspective view of a webbing retractor to which afirst embodiment of the lock mechanism according to the presentinvention is applied. In this webbing retractor, a frame 10 is securedto a vehicle body by mounting bolts (not shown). The frame 10 has a pairof parallel leg plates 12 and 14 extending from both sides thereof.

The leg plates 12 and 14 rotatably support a webbing takeup shaft 20which is also shown in FIG. 2. The takeup shaft 20 has at its center athrough-hole 22 extending radially thereof. One end of an occupantrestraining webbing (not shown) is retained by the through-hole 22. Thewebbing is wound up in layers on the takeup shaft 20. A tongue plate issecured to the other end portion of the webbing. An occupant of thevehicle engages the tongue plate with a buckle device which is securedto the vehicle body, whereby it is possible for the occupant to befastened by an intermediate portion of the webbing.

The takeup shaft 20 is composed of a core bar 20A which is formed of athick-walled plate material and a synthetic resin layer 20B which isintegrally formed around the core bar 20A by means of molding in such amanner that the takeup shaft 20 has a cylindrical external shape.

One end portion of the core bar 20A projects from one of thelongitudinal ends of the synthetic resin layer 20B such as to provide aprojecting portion 20C. The other end of the synthetic resin layer 20Bprojects from the leg plate 14. A spiral spring retractor (not shown) isinterposed between the synthetic resin layer 20B and the leg plate 14 insuch a manner that the takeup shaft 20 is biased in the webbing wind-updirection.

Lock plates 24 and 25 (shown in FIG. 1) which serve as lock members aredisposed around the projecting portion 20C. Each of the lock plates 24and 25 has a substantially U-shaped notched recess 26 formed in itscenter, thus having a substantially C-shaped form as a whole. Theprojecting portion 20C of the takeup shaft 20 is received in the notchedrecesses 26, thereby allowing the lock plates 24 and 25 to rotatetogether with the takeup shaft 20. The width of each of the notchedrecesses 26 is made slightly larger than the width of the projectingportion 20C as shown in FIG. 3, thereby allowing the lock plates 24 and25 to rotate relative to the takeup shaft 20 by a predetermined angle.

A pawl portion 28 is formed at one end of the lock plate 24, and a pawlportion 30 at one end of the lock plate 25. These pawl portions 28 and30 oppose the lock teeth of an internally-toothed ratchet wheel 32 whichis secured to the leg plate 12.

Further, a pair of pins 34 project from the lock plate 24, and a pair ofpins 36 from the lock plate 25. These pins 34 and 36 are respectivelyinserted into slots 40 which are formed in a lock ring 38. The lock ring38 is supported on a smaller-diameter shaft portion 20E which axiallyprojects from one end of the takeup shaft 20 in the central portion ofits circumference in such a manner that the lock ring 38 is rotatablerelative to the takeup shaft 20.

Moreover, a torsion coil spring 44 is interposed between the lock ring38 and a spring retainer pin 43 provided on a rotating wheel 42 which issecured to the distal end of the smaller-diameter shaft portion 20E. Thetorsion coil spring 44 is coaxially supported on the lock ring 38. Oneend of the spring 44 abuts against the spring retainer pin 43 of therotating wheel 42 while the other end abuts against a spring retainerpin 45 which projects from the lock ring 38. The lock ring 38 is biasedby means of the force of the torsion coil spring 44 such as to rotate inthe webbing wind-off direction (the direction of the arrow A in FIG. 1)of the takeup shaft 20. Accordingly, the lock ring 38 is normally biasedby means of the force of the torsion coil spring 44 such as to causeeach of the pins 34 and 36 of the lock plates 24 and 25 to be housed inone end portion of each of the slots 40, thus causing the pawl portions28 and 30 to be separated from the internally-toothed ratchet wheel 32as shown in FIG. 3.

However, when relative rotation occurs between the lock ring 38 and thetakeup shaft 20 which rotates in the webbing wind-off direction, thelock ring 38 has a rotational lag against the biasing force of thetorsion coil spring 44. At that time, the lock ring 38 causes the lockplates 24 and 25 to be guided in the longitudinal direction of the slots40, whereby the pawl portions 28 and 30 are engaged with theinternally-toothed ratchet wheel 32 in the manner shown in FIG. 4.

It is to be noted that the rotating wheel 42 has, as shown in FIG. 6, apair of retainer pawls 46 received in a rectangular bore 48 which isformed in the takeup shaft 20, whereby the rotating wheel 42 is retainedby the takeup shaft 20 and rotates together with the takeup shaft 20 inone unit.

A limiting plate 50 which serves as a limiting member is pivotallysupported on the outer periphery of the rotating wheel 42. The centralportion of a leaf spring 52 is pivotally supported at one portion of theinner periphery of the limiting plate 50. Both end portions 52A and 52Bof the leaf spring 52 are brought into resilient contact with the outerperiphery of the rotating wheel 42, whereby the limiting plate 50receives the rotational force of the rotating wheel 42 throughfrictional contact between the end portions 52A and 52B and the outerperiphery of the rotating wheel 42.

A pair of projections 54 and 56 radially project from the outerperiphery of the limiting plate 50. A pin 62 which projects from anactuator 60 of an acceleration sensing means 58 is inserted in the areabetween the projections 54 and 56. Thus, the movement of the pin 62 islimited by the limiting plate 50.

More specifically, the acceleration sensing means 58 includes a ballcasing 64 secured to the leg plate 12. The ball casing 64 houses a ball66 which serves as a rolling element. The ball 66 is received in aconical recess 68 which is formed in the ball casing 64 in such a mannerthat the ball 66 goes up the conical recess 68 when acceleration occurs.The actuator 60, which is pivotally supported by a bracket 70 through apin 72, is mounted on the ball 66. The arrangement is such that, whenthe ball goes up the conical recess 68, the actuator 60 is pivoted aboutthe pin 72, thus causing a pole 60A formed at the distal end of theactuator 60 to engage with one of the ratchet teeth 74 which are cut onthe outer periphery of the lock ring 38.

The pivoting angle or the range of pivotal movement of the limitingplate 50 is limited by the projection 54 which abuts against the pin 62and the projection 56 which abuts against an arm 64A which projects fromthe ball casing 64. Thus, the limiting plate 50 is adapted to be pivotalin such a manner that, when the takeup shaft 20 rotates in the webbingwind-off direction, the limiting plate 50 turns until the projection 56abuts against the arm 64A; when the takeup shaft 20 rotates in thewebbing wind-up direction, the limiting plate 50 turns until theprojection 54 abuts against the pin 62. The limiting plate 50 has aslanting cam surface 54A formed near the projection 54 such that, whenthe takeup shaft 20 rotates in the webbing wind-up direction, theslanting cam surface 54A pushes down the pin 62, thus causing the pole60A to be separated from the ratchet tooth 74 with which it has beenengaged in the manner shown in FIG. 7(D).

It is to be noted that a stopper plate 75 is, as shown in FIG. 1,secured to the rotating wheel 42 by a screw 76, thereby preventing thelimiting plate 50 from coming off the rotating wheel 42. Further, theinternally-toothed ratchet wheel 38, the rotating wheel 42 and so forthare covered with a cover 90 which is secured to the outside of the legplate 12.

The following is a description of the operation of this embodiment.

When the vehicle is in a normal state, the limiting plate 50 is in thecondition shown in FIG. 7(A), in which the ball 66 does not push up theactuator 60. In consequence, the actuator 60 is separated from theratchet teeth 74 irrespective of the pivotal movement of the limitingplate 50. For this reason, it is possible for the occupant who isfastened by the webbing to freely wind the webbing onto or off thetakeup shaft 20 so as to be able to assume a desired driving posture.

When the vehicle is in an emergency situation such as a collision, theball 66 pushes up the actuator 60 in such a manner that the actuator 60pivots about the pin 72. Consequently, the pole 60A is engaged with oneof the ratchet teeth 74.

On the other hand, the occupant is moved in the direction in whichacceleration acts. The webbing is therefore wound off from the takeupshaft 20, causing the takeup shaft 20 to rotate in the clockwisedirection as viewed in FIG. 7. In consequence, the lock ring 38 whichrotates together with the takeup shaft 20 is prevented from rotating bymeans of the actuator 60, which fact causes relative rotation betweenthe lock ring 38 and the takeup shaft 20. This relative rotation causesthe torsion coil spring 44 to be deformed as shown in FIG. 7(C), and thepins 34 and 36 of the lock plates 24 and 25 which rotate together withthe takeup shaft 20 are guided by the respective slots 40 formed in thelock ring 38 in such a manner that the pawl portions 28 and 30 areengaged with the internally-toothed ratchet wheel 32, whereby the takeupshaft 20 is prevented from rotating in the webbing wind-off direction.As a result, the occupant is brought into a reliable webbing restrainedcondition.

When the vehicle is running on a rough road with many irregularities,the ball 66 is held in a state wherein it continuously pushes up theactuator 60. At the same time, the occupant is bumped up and down by thevibration of the vehicle body, and the webbing is therefore repeatedlywound in and out on the takeup shaft 20.

On such an occasion, in the conventional webbing retractor, every timethe webbing is wound up, the lock ring 38 rotates counterclockwise fromthe position shown in FIG. 7(C) by an amount corresponding to one ormore ratchet teeth 74 and then reengages with the actuator 60, whichfact disadvantageously causes the webbing to be gradually wound up ontothe takeup shaft 20. More specifically, in the case where the racthettooth 74A is engaged with the pole 60A in the state shown in FIG. 7(C),the vibration of the vehicle may cause the ratchet tooth 74B or 74C tobe engaged with the pole 60A, and the webbing is thereby gradually woundup onto the takeup shaft 20.

In the present invention, however, the above-described problem is solvedby the provision of the limiting plate 50. More specifically, as shownin FIG. 7(D), when the limiting plate 50 is pivoted by the force derivedfrom the rotation of the takeup shaft 20 in the webbing wind-updirection, the slanting cam surface 54A pushes down the pin 62 of theactuator 60, thus causing the pole 60A to be separated from the ratchetteeth 74. In consequence, the lock ring 38 which is being biased bymeans of the force of the compressed torsion coil spring 44 is turned inthe clockwise direction by virtue of the biasing force of the spring 44in the manner shown in FIG. 7(E). Accordingly, the pin 62 of theactuator 60 which has opposed the ratchet tooth 74A now opposes theratchet tooth 74N.

Even if, thereafter, the takeup shaft 20 is further rotated in thewebbing wind-off direction as the result of the vibration of thevehicle, the pole 60A of the actuator 60 engages with the ratchet tooth74M or 74N. Consequently, the takeup shaft 20 is locked in the statewherein it has further rotated in the webbing wind-off direction fromthe position in the previous locked state by an amount which correspondsto one or more ratchet teeth 74. There is therefore no risk of thewebbing being gradually wound up onto the takeup shaft 20.

Thus, this embodiment involves no fear of the webbing being graduallywound up onto the takeup shaft even when the vehicle is running on arough road. It is therefore possible for the occupant to maintaindriving comfort.

Referring next to FIG. 8, there is shown a limiting plate 78 which isemployed in a second embodiment of the present invention. This limitingplate 78 is adapted to serve also as the rotating wheel 42 employed inthe above-described embodiment. Accordingly, the limiting plate 78 ispivotally supported on the smaller-diameter shaft portion 20E of thetakeup shaft 20, and both end portions 52A and 52B of the leaf spring 52are disposed such as to receive rotational force from thesmaller-diameter shaft portion 20E through frictional contacttherebetween in a manner similar to that of the first embodiment.

FIG. 9 shows a spring plate 80 which is employed in a third embodimentof the present invention in place of the limiting plates 50 and 78 whichare respectively employed in the first and second embodiments. Thisspring plate 80 is formed by bending a leaf spring into a substantiallyU-shape. The central portion of the spring plate 80 is brought intoresilient contact with the smaller-diameter shaft portion 20E of thetakeup shaft 20 shown in FIG. 1 such as to receive the rotational forceof the takeup shaft 20, and both end portions 80A and 80B of the springplate 80 respectively oppose the pin 62 and the arm 64A of the actuator60 so that the end portions 80A and 80B respectively serve as theprojections 54 and 56 in the above-described embodiments. The springplate 80 is also formed with a slanting surface 80C which is similar tothe slanting cam surfaces 54A in the above-described embodiments.

Referring next to FIG. 10, there is shown a fourth embodiment of thepresent invention. In this embodiment, a lock ring 38A is engaged with ascrew 82 which is formed at the axial end portion of the takeup shaft20. The lock ring 38A is moved axially of the takeup shaft 20 whenrelative rotation occurs between the lock ring 38A and the takeup shaft20 as the result of the engagement between the pole 60A of the actuator60 and one of the projections 38B which are formed on the outerperiphery of the lock ring 38A. In consequence, ratchet teeth 24A whichare formed at one axial end of the lock ring 38A such as to serve as alock member are engaged with lock teeth 32A which are formed on the legplate 12, whereby the rotation of the takeup shaft 20 is prevented. Thelock ring 38A is biased by the action of a compression coil spring 83 inthe direction in which the lock ring 38A separates from the leg plate12.

In this embodiment also, the actuator 60 which engages with the lockring 38A is separated from the lock ring 38A when the webbing is woundup by the action of the limiting plate 50 which receives the rotationalforce of the takeup shaft 20 through frictional contact. It is thereforepossible to obtain effects similar to those which are offered by theother embodiments described above.

The following is a description of a fifth embodiment of the presentinvention with reference to FIGS. 11 and 12.

In this embodiment, stopper pins 63A and 63B project from the leg plate12 secured to the frame 10. The limiting plate 50 in this embodiment isprovided with a cam projection 354 in place of the pair of projections54 and 56 shown in FIG. 1, the cam projection 354 radially projectingfrom the outer periphery of the plate 50 and having a predeterminedcircumferential length. The outer periphery of the cam projection 354opposes the pin 62 projecting from the actuator 60 of the accelerationsensing means 58 such as to limit the movement of the actuator 60 in amanner similar to that of the first embodiment. The outer periphery ofthe cam projection 54 also opposes the stopper pins 63A and 63B such asto limit the pivoting angle of the limiting plate 50.

Accordingly, the limiting plate 50 is adapted to be pivotal in such amanner that, when the takeup shaft 20 rotates in the webbing wind-offdirection, the limiting plate 50 turns until the cam projection 354abuts against the stopper pin 63A; when the takeup shaft 20 rotates inthe webbing wind-up direction, the limiting plate 50 turns until the camprojection 354 abuts against the stopper pin 63B.

The cam projection 354 is adapted such that, when the takeup shaft 20rotates in the webbing wind-off direction in response to the wind-off ofthe webbing 23 as shown in FIG. 13(A), the cam projection 354 separatesfrom the pin 62, thus allowing the pole 60A to engage with one of theratchet teeth 74; when the takeup shaft 20 rotates in the webbingwind-up direction as shown in FIG. 13(B), the cam projection 354 pushesdown the pin 62, thus causing the pole 60A to be separated from theratchet tooth 74 with which it has been engaged.

The arrangement is such that, in the case where the pole 60A of theactuator 60 is engaged with one of the ratchet teeth 74 in the stateshown in FIG. 13(A), even if the takeup shaft 20 rotates in the webbingwind-up direction, the cam projection 354 does not immediately push downthe pin 62. More specifically, when the webbing 23 is wound off by theaction of acceleration in the state wherein the ball 66 causes the pole60A to engage with one of the ratchet teeth 74, the webbing 23 is woundoff while the lock ring 38 is at rest, and the state of the lock plates24 and 25 changes from that shown in FIG. 3 to that shown in FIG. 4. Inother words, the lock plates 24 and 25 are engaged with theinternally-toothed ratchet wheel 32, whereby the wind-off of the webbing23 is suspended. Thereafter, when the webbing 23 is wound up, thereverse operation takes place. More specifically, the webbing 23 iswound up while the lock ring 38 is at rest, and the lock plates 24 and25 are separated from the internally-toothed ratchet wheel 32 to reachthe state shown in FIG. 3. Thereupon, the lock ring 38 also starts torotate in the webbing wind-up direction. At this time the pole 60A isreleased from the engagement with the lock ring 38. The rotational angleof the cam projection 354 is set such that, after the engagement betweenthe pole 60A and the lock ring 38 has been cancelled, the cam projection354 pushes down the actuator 60. Accordingly, the arrangement is suchthat the cam projection 354 abuts against the pin 62 of the actuator 60which is engaged with the lock ring 38 after the rotating wheel 42 hasrotated a predetermined angle in the counterclockwise direction from theposition shown in FIG. 13(A). This angle equals the amount by which thetakeup shaft 22 rotates in order for the pole 60A to be released fromengagement with the lock ring 38 and brought into light contact with thelock ring 38 or into a position slightly separated therefrom.

Thus, when the takeup shaft 22 rotates in the webbing wind-up direction,the pole 60A is released from its engagement with the ratchet tooth 74of the lock ring 38 with which it has been engaged. However, when thevehicle is running on a rough road, since the ball 66 is then held atits raised position, the pole 60A is also held at the position where itreengages with the lock ring 38 if the webbing 23 is wound off and thelock ring 38 is thereby caused to rotate in the webbing wind-offdirection. Accordingly, if the webbing 23 is further wound up, the camprojection 354 pushes down the actuator 60, thus causing the pole 60A tomove to a position (outside the locus of rotation of the lock ring 38)where the pole 60A cannot engage with the lock ring 38.

In this embodiment also, when the vehicle is running on a very roughroad, the ball 66 continuously pushes up the actuator 60. At the sametime, the occupant moves vertically in response to the vibration of thevehicle body, and the webbing is therefore repeatedly wound in and outon the takeup shaft 20.

However, the limiting plate 50 which pivots in response to the rotationof the takeup shaft 20 in the webbing wind-up direction causes the camprojection 354 to push down the pin 62 of the actuator 60 after theengagement between the pole 60A and the lock ring 38 has been cancelledas described above, whereby the pole 60A is separated from the ratchetteeth 74, as shown in FIG. 13(B). For this reason, even if the takeupshaft 20 is further rotated in the webbing wind-off direction as theresult of the vibration of the vehicle, the pole 60A of the actuator 60does not engage with the lock ring 38 unless the webbing is wound off bya length which corresponds to the circumferential length of the camprojection 354. Moreover, even if the webbing is wound off by a lengthwhich exceeds the length of the cam projection 354, since the pole 60Aengages with the same one of the ratchet teeth 74 of the lock ring 38 asthat in the previous engagement, there is no risk of the webbing beinggradually wound up on the takeup shaft 20.

Thus, this embodiment also involves no fear of the webbing beinggradually wound up even when the vehicle is running on a rough road. Itis therefore possible for the occupant to maintain driving comfort.

When the vehicle is running on a road in normal conditions, the takeupshaft 20 keeps the limiting plate 50 in the state shown in FIG. 13(B) bymeans of the wind-up force of the spiral spring, and the actuator 60 isconsequently pushed down. There is therefore no possibility of the ball66 generating any abnormal noise as the result of the vibration of thevehicle.

Referring now to FIG. 14, there is shown a limiting plate 378 which isemployed in a sixth embodiment of the present invention. This limitingplate 378 is adapted to serve also as the rotating wheel 42 in the firstembodiment. The limiting plate 378 is pivotally supported at thesmaller-diameter shaft portion 20E of the takeup shaft 20, and both endportions 52A and 52B of the leaf spring 52 are brought into resilientcontact with the smaller-diameter shaft portion 20E such as to receiverotational force from the shaft portion 20E through frictional contacttherebetween in a manner similar to that in the first embodiment.

FIG. 15 shows a spring plate 380 which is employed in a seventhembodiment of the present invention in place of the limiting plates 50and 378 which are respectively employed in the above-describedembodiments. This spring plate 380 is formed by bending a leaf spring.The spring plate 380 has its central portion brought into resilientcontact with the smaller-diameter shaft portion 20E of the takeup shaft20 shown in FIG. 1 such as to receive the rotational force of the takeupshaft 20. In addition, both end portions 380A and 380B of the springplate 380 are bent such as to provide in combination a function which issimilar to that of the cam projection 354 in the above-describedembodiments.

Referring next to FIG. 16, there is shown an eighth embodiment of thepresent invention. In this embodiment also, the lock ring 38A is engagedwith the screw 82 which is formed at one axial end portion of the takeupshaft 20. The lock ring 38A is moved axially of the takeup shaft 20 whenrelative rotation occurs between the lock ring 38A and the takeup shaft20 as the result of the engagement of the pole 60A of the actuator 60and one of the projections 38B formed on the outer periphery of the lockring 38A. In consequence, the ratchet teeth 24A which are formed at oneaxial end of the lock ring 38A such as to serve as a lock member areengaged with the lock teeth 32A formed on the leg plate 12, whereby therotation of the takeup shaft 20 is prevented. The lock ring 38A isbiased by the action of the compression coil spring 83 in the directionin which the lock ring 38A separates from the leg plate 12.

This embodiment is also arranged such that the actuator 60 which isengaged with the lock ring 38A is separated from the lock ring 38A whenthe webbing is wound up by the action of the cam projection 354 of thelimiting plate 50 which receives the rotational force of the takeupshaft 20 through frictional contact. Thus, it is possible to obtaineffects similar to those which are offered by the above-describedembodiments.

It is possible to alter as desired the circumferential length of the camprojection 354 provided on the limiting plate 50 in the above-describedembodiments. It is, however, preferable for the length of the camprojection 354 to correspond to the length (about 2 cm) of the webbing23 which is generally wound in and out repeatedly when the vehicle isrunning on a rough road.

Although in the above-described embodiments the limiting plate 50directly receives rotational force from the takeup shaft 20 throughfrictional contact, the present invention is not necessarily limitativein this respect and it is also possible to employ an arrangement whereinthe limiting plate 50 is pivoted through frictional contact between thesame and the lock ring 38, such as that in a ninth embodiment of thepresent invention which is shown in FIG. 17. In such a case, even if thewebbing is wound up in a locked state, the lock 38 rotates with arotational lag. The arrangement may, therefore, be such that thelimiting plate 50 immediately pushes down the actuator 60 in response tothe rotation of the lock ring 38.

In the ninth embodiment, the limiting plate 50 is pivotally supported ona collar 86 which is provided on the lock ring 38, and the leaf spring52 is brought into resilient contact with the outer periphery of thecollar 86, whereby the limiting plate 50 receives the rotational forceof the lock ring 38 through the frictional contact therebetween.

The following is a description of a tenth embodiment of the presentinvention with reference to FIGS. 18 to 20.

In this embodiment, the following members are employed in place of thecorresponding members in the first embodiment: a rotating cap 142 inplace of the rotating wheel 42; a friction spring 152 as a limitingmember in place of the limiting plate 50; and a cover 156 in place ofthe cover 90, the cover 156 having a pin 157 projecting from its innersurface.

The rotating cap 142 has, as shown in FIG. 21, a pair of retainer pawls146 engaged with the rectangular bore 48 formed in the takeup shaft 20,whereby the rotating cap 142 is retained by the takeup shaft 20 and isrotatable together therewith in one unit in a manner similar to that ofthe first embodiment.

The rotating cap 142 has the above-described friction spring 152 servingas a limiting member resiliently fitted on the outer peripheral surface150 thereof in such a manner that the rotational force of the rotatingcap 142 is transmitted to the friction spring 152 through the frictionalcontact therebetween. The friction spring 152 has its peripheral endportions 153 bent outwardly. It is therefore possible for the frictionspring 152 to be easily mounted on the rotating cap 142 by bringing theperipheral end portions 153 into contact with the outer peripheralsurface 150 and pressing the friction spring 152 toward the central axisof the rotating cap 142.

The friction spring 152 has a projection 154 projecting radially fromthe opposite end thereof relative to the peripheral end portions 153,the projection 154 being formed by bending the central portion of thespring 152. The projection 154 is adapted to separate the pole 60A ofthe actuator 60 from the ratchet teeth 74 when the webbing is wound up.

The pivoting angle of the friction spring 152 is limited by the range ofallowable movement of the projection 154 which abuts against the pin 62of the actuator 60 at one extremity of its movement and abuts againstthe pin 157 of the above-described cover 156 at the other extremity.Thus, the friction spring 152 is adapted to be pivotal in such a mannerthat, when the takeup shaft 20 rotates in the webbing wind-offdirection, the friction spring 152 turns until the projection 154 abutsagainst the pin 157; when the takeup shaft 20 rotates in the webbingwind-up direction, the friction spring 152 turns until the projection154 abuts against the pin 62. The projection 154 has a slanting camsurface 154A formed at its distal end. This slanting cam surface 154A isdesigned such that, when the takeup shaft 20 rotates in the webbingwind-up direction, the cam surface 154A pushes down the pin 62, thuscausing the pole 60A to be separated from the ratchet teeth 74, as shownin FIG. 22(D), in a manner similar to that in the first embodiment.

It is to be noted that the rotating cap 142 has collars 175 provided atboth ends of the outer peripheral surface 150, whereby the frictionspring 152 is prevented from coming off the rotating cap 142.

The operation of this embodiment will now be explained.

During normal running of the vehicle, as shown in FIG. 22(A), the ball66 is in a state wherein it does not push up the actuator 60, and theactuator 60 is therefore separated from the ratchet teeth 74irrespective of the rotation of the friction spring 152. For thisreason, it is possible for the occupant who is fastened by the webbingto freely cause the webbing to be wound in and out on the takeup shaft20 so that he may assume a desired driving posture.

When the vehicle is in an emergency situation such as a collision, theball 66 pushes up the actuator 60 in such a manner that the actuator 60pivots about the pin 72, thus causing the pole 60A to engage with one ofthe ratchet teeth 74.

On the other hand, the occupant is moved by means of inertia in theopposite direction relative to the direction in which acceleration acts,and the webbing is therefore wound off from the takeup shaft 20, causingthe latter to rotate in the clockwise direction as viewed in FIG. 22. Inconsequence, the lock ring 38 which rotates together with the takeupshaft 20 is prevented from rotating by the actuator 60, which factgenerates relative rotation between the lock ring 38 and the takeupshaft 20. This relative rotation causes the torsion coil spring 44 to bedeformed in the manner shown in FIG. 22(C). Consequently, the respectivepins 34 and 36 of the lock plates 24 and 25 which rotate together withthe takeup shaft 20 are guided by the associated slots 40 formed in thelock ring 38 in such a manner that the pawl portions 28 and 30 areengaged with the internally-toothed ratchet wheel 32, whereby therotation of the takeup shaft 20 in the webbing wind-off direction isprevented. As a result, the occupant is brought into a reliable webbingrestrained condition.

When the vehicle is running on a rough road with many irregularities,the ball 66 is placed in a state wherein it continuously pushes up theactuator 60. At the same time, the occupant is bumped up and down inresponse to the vibration of the vehicle body. For this reason, thewebbing is repeatedly wound in and out on the takeup shaft 20.

In such a case, in this embodiment, the friction spring 152, which ispivoted by means of the force of the takeup shaft 20 which rotates inthe webbing wind-up direction, pushes down the pin 62 of the actuator 60through the slanting cam surface 154A, thus causing the pole 60A toseparate from the ratchet tooth 74 with which it has been engaged, asshown in FIG. 22(D). In consequence, the lock ring 38, which is beingsubjected to the biasing force of the torsion coil spring 44 which hasbeen compressed, is rotated clockwise as shown in FIG. 22(E) by theurging of that biasing force. Accordingly, the pole 60A of the actuator60 which has opposed the ratchet tooth 74A now opposes the ratchet tooth74N.

Even if, thereafter, the takeup shaft 20 is rotated in the webbingwind-off direction as the result of the vibration of the vehicle, thepole 60A of the actuator 60 engages with the ratchet tooth 74M or 74N.In consequence, the takeup shaft 20 is locked in a state wherein it hasfurther rotated in the webbing wind-off direction from the previouslocked position by an amount which corresponds to the length of one ormore ratchet teeth 74. There is therefore no risk of the webbing beinggradually wound up on the takeup shaft 20.

Thus, this embodiment involves no fear of the webbing being graduallywound up onto the takeup shaft 20 even when the vehicle is running on arough road. Accordingly, it is possible for the occupant to drive thevehicle in a comfortable state even when the road condition isunfavorable.

Further, in this embodiment, the tightening prevention mechanism has asimple arrangement which is constituted by the rotating cap 142, thefriction spring 152 and the projections 157 and 62. Moreover, it ispossible for these constitutent elements to be extremely easilyassembled.

Referring next to FIG. 23, there is shown a friction spring 152A whichis employed in an eleventh embodiment of the present invention. Thefriction spring 152A is formed by bending a single metal wire. Incorrespondence with this friction spring 152A, the width of the outerperipheral surface 150 of the rotating cap 142 shown in FIG. 18 is madesmaller than that in the case of the tenth embodiment.

FIG. 24 shows a part of a twelfth embodiment of the present invention,in which the bracket 70 is extended such as to form a projecting end 57Awhich replaces the projection 157 shown in FIG. 20.

It is to be noted that the rotating cap 142 may be integrally formedwith the takeup shaft 22 by means of molding.

The following is a description of a thirteenth embodiment of the presentinvention with reference to FIG. 25.

This embodiment employs a friction spring 252 which has a configurationdifferent from that of the friction spring 152 employed in the tenthembodiment, and a pusher 254.

The rotating cap 142 has the friction spring 252 serving as a limitingmember resiliently fitted on its outer peripheral surface 150 in such amanner that the rotational force of the rotating cap 142 is transmittedto the friction spring 252 through frictional contact therebetween. Thefriction spring 252 has its peripheral end portions 253A and 253B bentoutwardly. Accordingly, it is possible for the friction spring 252 to beeasily mounted on the rotating cap 142 by bringing the peripheral endportions 253A and 253B into contact with the outer peripheral surface150 and pressing the friction spring 252 toward the central axis of therotating cap 142.

The peripheral end portion 253A of the friction spring 252 is curved ina cylindrical shape such as to pivotally and loosely support a pin 254Awhich is provided on the pusher 254. The pin 254A projects from onevertex of the triangular pusher 254. The pusher 254 further has a bore254B formed at another vertex thereof, and a pin 255 which projects fromthe leg plate 12 is fitted into the bore 254B. Accordingly, when thefriction spring 252 moves pivotally, the pusher 254 is pivoted about thepin 255.

The pusher 254 has a curved pressing piece 254C projecting therefrom insuch a manner that it is possible for the pressing piece 254C to pressdown an arm 60B of the actuator 60.

The pivoting angle of the friction spring 252 is limited within therange of allowable movement of the pressing piece 254 which abutsagainst the arm 60B on one side and abuts against the pin 157 projectingfrom the inner surface of the cover 156 on the other. Thus, when thetakeup shaft 20 rotates in the webbing wind-off direction, the pusher254 pivots until the pressing piece 254C abuts against the pin 157; whenthe takeup shaft 20 rotates in the webbing wind-up direction, thepressing piece 254C abuts against the arm 60B and pushes down thelatter, thus causing the pole 60A to separate from the ratchet teeth 74in the manner shown in FIG. 26(D).

The operation of this embodiment will now be explained.

When the vehicle is running in normal conditions, the ball 66 is in astate wherein it does not push up the actuator 60, and the actuator 60is therefore separated from the ratchet teeth 74 irrespective of therotation of the friction spring 252, as shown in FIG. 26(A).Accordingly, it is possible for the occupant who is fastened by thewebbing to freely cause the webbing to be wound in and out on the takeupshaft 20 so that he may assume a desired driving posture.

When the vehicle is in an emergency situation such as a collision, theball 66 pushes up the actuator 60 in such a manner that the actuator 60pivots about the pin 72. In consequence, the pole 60A is engaged withone of the ratchet teeth 74.

On the other hand, the occupant is moved by means of inertia in theopposite direction relative to the direction in which accleration acts,and the webbing is therefore wound off from the takeup shaft 20, causingthe latter to rotate in the clockwise direction as viewed in FIG. 26. Inconsequence, the rotation of the lock ring 38 which rotates with thetakeup shaft 20 is prevented by the actuator 60, which fact generatesrelative rotation between the lock ring 38 and the takeup shaft 20. Thisrelative rotation causes the torsion coil spring 44 to be deformed orcompressed as shown in FIG. 26(C), and the respective pins 34 and 35 ofthe lock plates 24 and 25 which rotate together with the takeup shaft 20are guided by the associated slots 40 formed in the lock ring 38 in sucha manner that the pawl portions 28 and 30 are engaged with theinternally-toothed ratchet wheel 32, whereby the rotation of the takeupshaft 20 in the webbing wind-off direction is prevented. As a result,the occupant is brought into a reliable webbing restrained condition.

When the vehicle is running on a rough road with many irregularities,the ball 66 is placed in a state wherein it continuously pushes up theactuator 60. At the same time, the occupant is bumped up and down inresponse to the vibration of the vehicle body. In consequence, thewebbing is repeatedly wound in and out on the takeup shaft 20.

On such an occasion, in the conventional webbing retractor, every timethe webbing is wound up, the lock ring 38 rotates counterclockwise fromthe position shown in FIG. 26(C) by an amount which exceeds the lengthof one of the ratchet teeth 74 and then reengages with the actuator 60,thus causing the webbing to be gradually wound up onto the takeup shaft20. More specifically, in the case where the ratchet tooth 74A isengaged with the pole 60A in the state shown in FIG. 26(C), thevibration of the vehicle causes the ratchet tooth 74B or 74C to beengaged with the pole 60A, which fact involves a risk of the webbingbeing gradually wound up onto the takeup shaft 20.

This embodiment, however, overcomes the above-described disadvantage ofthe prior art. More specifically, as shown in FIG. 26(D), the pusher 254is pivoted clockwise by the action of the friction spring 252 which isturned in response to the rotation of the takeup shaft 20 in the webbingwind-up direction. In consequence, the pressing piece 254C pushes downthe arm 60B of the actuator 60, thus causing the pole 60A to separatefrom the ratchet teeth 74. Accordingly, the lock ring 38, which is beingsubjected to the biasing force of the torsion coil spring 44 which hasbeen compressed, is rotated clockwise as shown in FIG. 26(E) by theurging of that biasing force. Consequently, the pole 60A of the actuator60 which has opposed the ratchet tooth 74A now opposes the ratchet tooth74N.

Even if, thereafter, the takeup shaft 20 is rotated in the webbingwind-off direction as the result of the vibration of the vehicle, thepole 60A of the actuator 60 engages with the ratchet tooth 74M or 74N.In consequence, the takeup shaft 20 is locked in a state wherein it hasfurther rotated in the webbing wind-off direction from the previouslocked position by an amount which corresponds to one or more ratchetteeth 74. There is therefore no risk of the webbing being graduallywound up onto the takeup shaft 20.

Thus, this embodiment involves no fear of the webbing being graduallywound up onto the takeup shaft 20 even when the vehicle is running on arough road. It is therefore possible for the occupant to drive thevehicle in a comfortable state.

Further, since the pressing piece 254C is adapted to press against thearm 60B of the actuator 60 in the direction substantially orthogonal tothe plane of the arm 60B of the actuator 60, the pressing piece 254C isable to apply a large torque to the actuator 60. It is thereforepossible to cause the pole 60A to be reliably separated from the ratchetteeth 74.

Furthermore, the disposition of the pressing piece 254C in relation tothe arm 60B is such as that shown in FIG. 27(A), and the pressing piece254C is curved. It is therefore possible for this arrangement to beemployed even when the frame 10 is secured to the vehicle body at aninclination (i.e., the takeup shaft 20 is disposed in an inclined statewith respect to the horizontal). More specifically, provided that theacceleration sensor 58 is horizontally disposed (such an accelerationsensor is referred to as an "inclined condition acceleration sensor"),even if the disposition of the pressing piece 254C in relation to thearm 60B is such as that shown in FIG. 27(B), it is still possible forthe pressing piece 254C to press against the arm 60B in the directionsubstantially orthogonal to the plane of the arm 60B. For this reason,it is possible to employ pushers 254 with the same configurationirrespective of the type of inclined condition acceleration sensoremployed (it is general practice to employ one of the five differenttypes of sensors which respectively cope with inclination angles of-10°, -5°, 0°, 5° and 10°). Thus, it is possible to reduce theproduction cost as a whole.

The following is a description of a fourteenth embodiment of the presentinvention with reference to FIG. 28.

The fourteenth embodiment employs a pusher 278 which is formed bybending a rod. More specifically, the upper end portion 278A of thepusher 278 is bent at 90° and pivotally supported by the peripheral endportion 253A of the friction spring 252. The pusher 278 has itsintermediate portion guided by guide pins 280 which project from thecover 156 (see FIG. 25) in such a manner that the pusher 278 isvertically movable. The lower end portion of the pusher 278 is bent at90° toward the pole 60A, and the lower part of the lower end portion ofthe pusher 278 is further bent at 90° in the direction orthogonal to theplane of the arm 60B, whereby the torque applied to the arm 60B isincreased. In the case where the takeup shaft 20 rotates in the webbingwind-off direction, when the friction spring 252 pivots by apredetermined angle, the peripheral end portion 253B of the spring 252abuts against a stopper pin 282 which is provided on the cover 156 (seeFIG. 25), whereby the pivoting angle of the friction spring 252 islimited. The other points are similar to those in the eighth embodiment.

It is to be noted that the projection 157 in the thirteenth embodimentand the stopper pin 282 in the fourteenth embodiment may be omitted.

The present invention may be applied to all types of lock mechanisms inwhich, when a vehicular emergency occurs, the lock ring rotates relativeto the takeup shaft, and the lock member is thereby engaged with thelock teeth provided on the frame, thus preventing the rotation of thetakeup shaft in the webbing wind-off direction.

It is, as a matter of course, possible to employ structures exclusive ofthe above-described ball as the acceleration sensing means of thepresent invention.

What is claimed is:
 1. A lock mechanism for a webbing retractor which isemployed in a seatbelt system for a vehicle and adapted to wind up anoccupant restraining webbing onto a webbing takeup shaft by means of abiasing force, which comprises:(a) lock means adapted to prevent therotation of said takeup shaft in the webbing wind-off direction when avehicle emergency occurs, said lock means including a lock ringsupported on said takeup shaft; (b) acceleration sensing means includingan actuator adapted to engage with said lock ring to prevent therotation of said takeup shaft in the webbing wind-off direction when avehicular emergency occurs; and (c) limiting means for preventingengagement between the lock means and the accelerator sensing means whenno vehicular emergency is occurring, said limiting means havingfrictional contact means, canacelling means and pivoting limiting means,wherein said limiting means is pivotally movable around the takeup shaftthrough the frictional contact of said friction contact means, saidcancelling means includes a first leg member that is moved in a firstdirection in response to the pivoting of said frictional contact meansand adapted to prevent a locked state of said lock means when saidtakeup shaft rotates in the webbing wind-up direction, and said pivotinglimiting means includes a second leg member that is pivotally movablearound the takeup shaft in a second direction when the takeup shaftrotates in a webbing wind-out direction to limit the pivoting range ofsaid limiting means, whereby said webbing is prevented from beinggradually wound up onto takeup shaft when said vehicle is running.
 2. Alock mechanism according to claim 1, wherein said limiting meansincludes a cam surface constituting said cancelling means which isadapted to force said actuator to disengage from said lock ring whensaid takeup shaft rotates in the webbing wind-up direction.
 3. A lockmechanism according to claim 2, wherein said limiting means includes aring-shaped limiting plate which is disposed in coaxial relation to saidtakeup shaft and has said frictional contact means provided on its innerperipheral surface, said limiting plate further having on its outerperipheral surface a cam surface which constitutes said cancellingmeans, and said actuator has an abutting member adapted to abut againstsaid cam when said takeup shaft rotates in the webbing wind-updirection, thereby moving said actuator in the direction in which it isseparated from said lock ring.
 4. A lock mechanism according to claim 3,wherein said pivoting limiting means is constituted by projections whichrespectively project from both sides of said cam surface, while theabutting member of said actuator is a pin which projects from saidactuator, said pin being disposed between said projections, therebylimiting the pivoting range of said limiting means.
 5. A lock mechanismaccording to claim 4, wherein said limiting plate is brought intofrictional contact with said takeup shaft through the outer peripheralsurface of a smaller-diameter portion of a hat-shaped rotating platewhich is secured to one end portion of said takeup shaft.
 6. A lockmechanism according to claim 3, wherein said limiting means includes aspring plate having a C-shaped portion which constitutes said frictionalcontact means and a pair of leg portions which respectively extend fromboth ends of said C-shaped portion, one of said leg portions having saidcam surface formed in the vicinity of the end thereof, said cam surfacebeing adapted to abut against the abutting member of said actuatorthereby to separate said actuator from said lock ring.
 7. A lockmechanism according to claim 6, wherein said pivoting limiting means isconstituted by said leg portions, while said abutting member of saidactuator is a pin which projects from said actuator, said pin beingdisposed between said leg portions, thereby limiting the pivoting rangeof said limiting means.
 8. A lock mechanism for a webbing retractorwhich is employed in a seatbelt system for a vehicle and adapted to windup an occupant restraining webbing onto a webbing takeup shaft by meansof a biasing force, which comprises:(a) lock means adapted to preventthe rotation of said takeup shaft in the webbing wind-off direction whena vehicle emergency occurs, said lock means including a lock ringsupported on said takeup shaft; (b) acceleration sensing means adaptedto acutate said lock means when a vehicular emergency occurs, therebypreventing the rotation of said takeup shaft in the webbing wind-offdirection, wherein said acceleration sensing means includes an actuatoradapted to engage with said lock ring to prevent the rotation of thetakeup shaft in the webbing wind-off direction, and (c) limiting meanshaving frictional contact means constituted by a substantially C shapedfriction spring and a cancelling means including a pusher having asubstantially triangular cross-section, said pusher being pivotallysupported at one vertex thereof in such a manner that the longitudinalaxis of said pusher extends in parallel to the axial direction of saidtakeup shaft, said pusher being connected at another vertex thereof tosaid frictional contact means such that said pusher pivots about itsfirst-described vertex in response to the pivoting of said frictionspring, and said pusher having a pressing piece which abuts against saidactuator in a direction substantially orthogonal to the plane of saidactuator when said takeup shaft rotates in the webbing wind-updirection, thus causing said actuator to be separated from said lockring, whereby said webbing is prevented from being gradually wound uponto said takeup shaft when said vehicle is running.
 9. A lock mechanismfor a webbing retractor which is employed in a seatbelt system for avehicle and adapted to wind up an occupant restraining webbing onto awebbing takeup shaft by means of a biasing force, which comprises:(a)lock means adapted to prevent the rotation of said takeup shaft in thewebbing wind-off direction when a vehicle emergency occurs, said lockmeans including a lock ring supported on said takeup shaft; (b)acceleration sensing means adapted to actuate said lock means when avehicular emergency occurs, thereby preventing the rotation of saidtakeup shaft in the webbing wind-off direction, wherein saidacceleration sensing means includes an actuator adapted to engage withsaid lock ring to prevent the rotation of the takeup shaft in thewebbing wind-off direction, and (c) limiting means having frictionalcontact means constituted by a substantially C-shaped friction springand cancelling means including a pusher, said frictional contact meanstransmitting the rotational force of said webbing takeup shaft throughfrictional contact, wherein said pusher is constituted by a rod which issuspended from one end of said C-shaped friction spring, said rod beingmoved in the direction in which said rod comes in and out of contactwith said actuator when said friction spring pivots while being guidedby guide members which are respectively disposed on both sides of saidrod, whereby said webbing is prevented from being gradually wound uponto said takeup shaft when said vehicle is running.
 10. A lockmechanism employed in a webbing retractor which has a takeup shaftadapted to wind up an occupant restraining webbing thereof and means forbiasing the takeup shaft in the webbing wind-up direction, whichcomprises:(a) lock means including a lock ring which is disposed incoaxial relation to said webbing takeup shaft and adapted to rotatetogether with the rotation of said takeup shaft in the webbing wind-offdirection, said lock means being adapted to prevent the rotation of saidtakeup shaft in the webbing wind-off direction when a vehicularemergency occurs; (b) acceleration sensing means including actuatoradapted to engage with said lock ring when a vehicluar emergency occursthereby to prevent the rotation of said takeup shaft in the webbingwind-off direction; and (c) limiting means including frictional contactmeans, separating means and pivot limiting means wherein the separatingmeans is pivotally connected to a pin means displaced from said takeupshaft, and wherein said frictional contact means transmits therotational force of said takeup shaft through frictional contact to saidseparating means to pivot it, and wherein said separating means abutsagainst said actuator when said takeup shaft rotates in the webbingwind-up direction thus causing said actuator to be separated from saidlock ring, and said pivot limiting means includes a pin means forlimiting the pivoting range of said separating means, whereby saidwebbing is prevented from being gradually wound up onto said takeupshaft when the vehicle is running so as to avoid any undesirabletightening of said webbing against the body of the occupant of thevehicle.
 11. A lock mechanism according to claim 10, wherein saidfrictional contact means is constituted by a resilient member.
 12. Alock mechanism according to claim 10, wherein said limiting meansincludes: a C-shaped portion which constitutes said frictional contactmeans; a pair of leg portions respectively extending from both ends ofsaid C-shaped portion such as to constitute in combination said pivotinglimiting means; and a cam portion formed on one of said leg portions inthe vicinity of the end thereof such as to constitute said separatingmeans.
 13. A lock mechanism employed in a webbing rectractor which has atakeup shaft adapted to wind up an occupant restraining webbing thereonand means for biasing the takeup shaft in the webbing wind-up direction,which comprises:(a) lock means including a lock ring which is disposedin coaxial relation to said webbing takeup shaft and adapted to rotatetogether with the rotation of said takeup shaft in the webbing wind-offdirection, said lock means being adapted to prevent the rotation of saidtakeup shaft in the webbing wind-off direction when a vehicularemergency occurs; (b) acceleration sensing means including an actuatoradapted to engage with said lock ring when a vehicular emergency occursthereby to prevent the rotation of said takeup shaft in the webbingwind-off direction; and (c) limiting means including frictional contactmeans constituted by a substantially C-shaped friction spring, andseparating means including a pusher, wherein said pusher has asubstantially triangular cross section, said pusher being pivotallysupported at one vertex thereof in such a manner that the longitudinalaxis of said pusher extends in parallel to the axial direction of saidtakeup shaft, said pusher being connected at another vertex thereof tosaid frictional contact means such that said pusher pivots about itsfirst-described vertex in response to the pivoting of said frictionspring, and said pusher having a pressing piece which abuts against saidactuator in a direction substantially orthogonal to the plane of theactuator when said takeup shaft rotates in the webbing wind-updirection, thus causing said actuator to be separated from said lockring, whereby said webbing is prevented from being gradually wound uponto said takeup shaft when the vehicle is running so as to avoid anyundesirable tightening of said webbing against the body of the occupantof the vehicle.
 14. A lock mechanism employed in a webbing retractorwhich has a takeup shaft adapted to wind up an occupant restrainingwebbing thereon and means for biasing the takeup shaft in the webbingwind-up direction, which comprises:(a) lock means including a lock ringwhich is disposed in coaxial relation to said webbing takeup shaft andadapted to rotate together with the rotation of said takeup shaft in thewebbing wind-off direction, said lock means being adapted to prevent therotation of said takeup shaft in the webbing wind-off direction when avehicluar emergency occurs; (b) acceleration sensing means including anacutator adapted to engage with said lock ring when a vehicularemergency occurs thereby to prevent the rotation of said takeup shaft inthe webbing wind-off direction; and (c) limiting means includingfrictional contact means constituted by a substantially C-shapedfriction spring, and separating means including a pusher wherein saidpusher is constituted by a rod which is suspended from one end of saidC-shaped friction spring, said rod being moved in a directionsubstantially orthogonal to the plane of said actuator when said shaftrotates in the webbing wind-up direction, and in which said rod comes inand out of contact with said actuator when said friction spring pivotswhile being guided by guide members which are respectively disposed onboth sides of said rod, thus causing said actuator to be separated fromsaid lock ring, whereby said webbing is prevented from being graduallywound up onto said takeup shaft when the vehicle is running so as toavoid any undesirable tightening of said webbing against the body of theoccupant of the vehicle.